As a mechanical hand of the above-mentioned type, there has been known one as disclosed in, for instance, Japanese Unexamined Patent Publication No. 3052/1984.
The mechanical hand is adapted to process a curved plate 1 consisting of two curved glass plates 2 (i.e. 2a and 2b) and an intermediary film 3 interposed between the two glass plates; particularly, to cut the end portion of the intermediary film 3 which extends from the end portions of the glass plates as shown in FIG. 11. The basic construction of the mechanical hand is such that a fixed bracket 5 is fixed to a hand supporting member 4a formed at an end of a robot arm 4. A processing tool 6 such as a rotating endless cutting blade is mounted on the fixed bracket 5, whereby the end portion of the intermediary film 3 is subjected to a cutting process at a point of processing P of the processing tool 6 by previously teaching the sequential operations of the robot.
In the conventional mechanical hand for processing edges of the curved plate, when the mechanical hand is mounted on a robot operable in an orthogonal coordinate axis system to cut the edge of the intermediary film 3, if a flat plate 1' as indicated by an imaginary line is to be processed for cutting of its edge portion, it is sufficient that, as shown by another imaginary line in FIG. 11, each coordinate point (X, Y, Zo in FIG. 11) of the hand supporting member 4a of the robot arm 4 corresponds to each coordinate point (X, Y, Z in FIG. 11) of the point of processing P. However, when the end portion of the curved plate 1 is to be cut, it is insufficient to obtain an expected result by specifying a position in the coordinate system for the hand supporting member 4a, and it is necessary to determine the posture in tilting of the processing tool 6 so as to correspond to an angle of inclination of the edge portion of curved plate 1. Accordingly, it is necessary to specify an angle of rotation .alpha. around the axial line (corresponding to the Z axis) and an angle of rotation .beta. around an axis orthogonal to the axial line of the hand supporting member 4a of the robot arm 4.
Under such circumstances, in order to tilt the processing tool 6 by the angle of rotation .beta. at a position where the processing tool 6 is rotated by the angle of rotation .alpha. to thereby conduct a teaching operation for the robot, it is necessary to adjust the coordinate points (X, Y, Zo) of the hand supporting member 4a in correspondence to each factor of displacement .DELTA.X, .DELTA.Y and .DELTA.Z in addition to tilting the hand supporting member 4a of the robot arm 4 by the angle of rotation .beta.. This causes a complicated teaching operation because a locus in the teaching operation of the hand supporting member 4a can not be utilized for processing the edge portion of the curved plate 1.
When the processing tool 6 is tilted in the operations of an industrial robot, it is sometimes necessary to limit an acceleration speed in each movement so as to stabilize the tilting movement of the processing tool because the movement of rotation of the hand supporting member 4a should be in association with the movements of displacement of the hand supporting member 4a in the coordinate system. The limitation of the acceleration speed of the hand supporting member 4a takes much time for processing the edge portion of the curved plate by the processing tool 6. Further, it is difficult to follow the posture of the processing tool in accordance with a sharp change in an angle of inclination of an edge portion of the curved plate 1 to be processed.